CD274 and neoplasm: These effects of PD-L1 expression or PD-L1-containing exosomes on tumor growth were accompanied by decreased proliferation (as measured by quantitative analysis of Ki-67 staining in the tumor cells) and a reduction in tumor-infiltrating lymphocytes (as measured by quantitative analysis of CD3 staining in the tumor microenvironment; Supplementary Fig. 7 and Fig. 4e, f).